1. Field of the Invention
The present invention relates to a process for producing a thermotropic liquid crystalline polymer having a flow beginning temperature of 340xc2x0 C. or more.
2. Description of the Related Art
Thermotropic liquid crystalline polymers are widely used as portable and thin electric and electronic parts materials due to excellent melt flowability and heat resistance.
Various methods are known for producing a thermotropic liquid crystalline resin.
For example, JP-A No. 2-69518 discloses a process for producing a whole aromatic polyester, and it is also disclosed that when a pre-polymer is polymerized in solid phase, it is necessary to select treating temperature and temperature raising speed so that particles of the resin are not sintered, and when sintered, polymerization is suppressed and removal of substances having low boiling point becomes insufficient.
Particularly, when producing a thermotropic liquid crystalline resin of high heat resistance having a flow beginning temperature of 340xc2x0 C. or more by solid phase polymerization, it is difficult to effect solid phase polymerization so that particles of the resin are not sintered, and even when sintering of resin particles is few, blistering occurs on the surface of a molded article containing said resin under high temperature for soldering and the like.
An object of the present invention is to provide a process for producing a thermotropic liquid crystalline resin having a flow beginning temperature of 340xc2x0 C. or more which does not cause sintering of resin particles in solid phase polymerization, and scarcely causes a problem of blistering of a molded article containing said resin under high temperature environment.
The present inventors have intensively studied to find a process for producing a thermotropic liquid crystalline resin having a flow beginning temperature of 340xc2x0 C. or more which has no problems as described above, and resultantly found that, a thermotropic liquid crystalline resin having a flow beginning temperature of 340xc2x0 C. or more can be produced without causing problems as described above by controlling the average temperature raising speed of resin temperature (t) in a specific range when raising the resin temperature (t) from (FT0+20)xc2x0 C. to (FT0+50)xc2x0 C. and controlling the flow beginning temperature of a thermotropic liquid crystalline resin at each resin temperature in a specific range, and have completed the present invention.
Namely, the present invention relates to a process for producing a thermotropic liquid crystalline polymer having a flow beginning temperature of 340xc2x0 C. or more comprising raising the temperature of a thermotropic liquid crystalline polymer from 200xc2x0 C. or less to raising end temperature (Axc2x0 C.) of (FT0+50)xc2x0 C. or more in substantially solid phase condition,
wherein the thermotropic liquid crystalline polymer has a flow beginning temperature (FT0) of 200xc2x0 C. or more and 300xc2x0 C. or less, and in a step of raising the resin temperature (t) from (FT0+20)xc2x0 C. to (FT0+50)xc2x0 C. (step (1)), the average raising speed of the resin temperature is from over 0.1xc2x0 C./min. to less than 0.5xc2x0 C./min. and the flow beginning temperature of the thermotropic liquid crystalline polymer at each resin temperature is (txe2x88x9210)xc2x0 C. or more and (t+40)xc2x0 C. or less.
Embodiments of the present invention are described below. In the following descriptions, xe2x80x9cheat resistancexe2x80x9d of a resin means a thermomechanical and chemical heat resistance. As measure of thermomechanical heat resistance, deflection temperature under load is exemplified. As measure of chemical heat resistance, soldering resistance is exemplified. xe2x80x9cProcessabilityxe2x80x9d of a resin means melt flowability of a resin in injection molding mainly.
The thermotropic liquid crystalline resin of the present invention is, for example, a whole aromatic thermotropic liquid crystalline resin such as polyesters or polyesteramides having a whole aromatic skeleton, and there are exemplified
(1) resins having a structural unit derived from at least one aromatic hydroxycarboxylic acids,
(2) resins having a structural unit derived from aromatic dicarboxylic acid and aromatic diol,
(3) resins having a structural unit derived from aromatic hydroxycarboxylic acid, aromatic dicarboxylic acid and aromatic diol,
(4) resins obtained by adding a structural unit derived from aromatic aminocarboxylic acid to (1),
(5) resins obtained by adding a structural unit derived from aminophenols to (2) and (3), and the like, and the thermotropic liquid crystalline resin usually forms an anisotropic melted body at temperatures of 400xc2x0 C. or less.
Examples of the structural unit of the above-mentioned polyesters or polyesteramides having a whole aromatic skeleton include, but not limited to, the following units.
Structural units derived from aromatic hydroxycarboxylic acid: 
Structural units derived from aromatic diol: 
Structural units derived from aromatic dicarboxylic acid: 
Structural units derived from aromatic aminocarboxylic acid: 
Structural units derived from aminophenols: 
The above-mentioned structural units derived from aromatic hydroxycarboxylic acid, aromatic diol, aromatic dicarboxylic acid, aromatic aminocarboxylic acid and aminophenols may have a substituent such as halogen atom, alkyl group, aryl group and the like on aromatic ring.
Among them, those having a total content of the above-mentioned structural units (I), (II), (III) and (IV) of 95 mol % or more are preferable from the standpoint of balance of heat resistance and processability, and those consisting essentially of the above-mentioned structural units (I), (II), (III) and (IV) are more preferable. Other structural units than (I), (II), (III) and (IV) can be appropriately selected from structural units derived from aromatic hydroxycarboxylic acid, aromatic diol, aromatic dicarboxylic acid, aromatic aminocarboxylic acid and aminophenols.
The molar ratio of (III)/(IV) is preferably from 8 to 50. When a thermotropic liquid crystalline resin having (III)/(IV) of less than 8 is used, it may be difficult to obtain a resin having a flow beginning temperature of 340xc2x0 C. or more without causing fusion of a resin even if polymerization is effected according to the present invention. When (III)/(IV) is over 50, processability may be poor. From the standpoint of balance of sufficient heat resistance and processability, (III)/(IV) is more preferably from 18 to 40, and further preferably from 15 to 30.
The molar ratio of (I)/((I)+(II)+(III)+(IV)) is preferably from 0.4 to 0.7. When (I)/((I)+(II)+(III)+(IV)) is less than 0.4, the heat resistance of the thermotropic liquid crystalline resin may lower. When over 0.7, processability may be poor. From the standpoint of balance of sufficient heat resistance and processability, (I)/((I)+(II)+(III)+(IV)) is further preferably from 0.45 to 0.55.
The molar ratio of (II)/((III)+(IV)) is preferably from 0.9 to 1.1. When (II)/((III)+(IV)) is less than 0.9 or over 1.1, it may be difficult to obtain a resin having a flow beginning temperature of 340xc2x0 C. or more without causing fusion of a resin even if polymerization is effected according to the present invention.
The objective of the present invention is to provide a thermotropic liquid crystalline resin having a flow beginning temperature of 340xc2x0 C. or more. From the standpoint of processability of the resin, the flow beginning temperature is preferably 400xc2x0 C. or less. When higher balance of heat resistance and processability is desired, the flow beginning temperature of the resin is more preferably from 370xc2x0 C. to 390xc2x0 C.
A process for producing a thermotropic liquid crystalline resin having a flow beginning temperature FT0 of 200xc2x0 C. or more and 300xc2x0 C. or less before initiation of temperature raising (hereinafter, this resin is sometimes referred to as pre-polymer) used in the present invention is not particularly restricted. There is exemplified a process in which a hydroxyl group and an amino group of aromatic hydroxycarboxylic acids, aromatic diols, aromatic aminocarboxylic acids or aromatic aminophenols are acylated with an acylating agent such as acetic anhydride and the like, and poly-condensation is effected together with aromatic dicarboxylic acids while distilling off unreacted acylating agents and an acid by-produced. It is preferable that the resulted poly-condensed substance is recovered in melted condition from a reaction vessel, solidified by cooling, then, ground to give a granule of a prepolymer, or solidified by cooling from melted condition into a string which is cut to give a pellet of a prepolymer.
In the present invention, a granule or pellet of a prepolymer has a particle diameter of preferably 10 mm or less, further preferably 5 mm or less. When the particle diameter of a granule or pellet is over 10 mm, it may be insufficient to remove substances having a lower boiling point such as an acid by-produced by poly-condensation when poly-condensation is conducted in solid phase.
An apparatus used in the present invention is not particularly restricted, and generally known heat treatment apparatuses and drying machines can be used. As examples thereof, a compartment oven, rotary kiln, fluidized bed type drier and the like are listed. It is preferable to use them under a nitrogen atmosphere.
The process for producing a thermotropic liquid crystalline polymer of the present invention is a process comprising raising the temperature of a thermotropic liquid crystalline polymer having a flow beginning temperature FT0 of 200xc2x0 C. or more and 300xc2x0 C. or less before initiation of temperature raising, from the temperature raising initiation temperature of 200xc2x0 C. or less to raising end temperature (Axc2x0 C.) of (FT0+50)xc2x0 C. or more in substantially solid phase condition. The characteristics of the present invention is that, in a step of raising the resin temperature (t) from (FT0+20)xc2x0 C. to (FT0+50)xc2x0 C. (step (1)), temperature raising is effected so that the average raising speed of the resin temperature is in the range of from over 0.1xc2x0 C./min. to less than 0.5xc2x0 C./min. and the flow beginning temperature of the thermotropic liquid crystalline polymer at each resin temperature is in the range of from (txe2x88x9240)xc2x0 C. or more to (t+10)xc2x0 C. or less. Preferably, in the step (1), raising speed of the resin temperature is substantially stable.
Here, the flow beginning temperature is a temperature at which when a resin heated at a temperature raising speed of 4xc2x0 C./min. is extruded from a nozzle having a internal diameter of 1 mm and a length of 10 mm under a load of 9.81 MPa, the melt viscosity shows a value of 4800 Paxc2x7s.
When the average temperature raising speed is 0.1xc2x0 C./min. or less, there may occur problems that the flow beginning temperature of a thermotropic liquid crystalline resin does not reach 340xc2x0 C. or more; a longer time is required for sufficiently progressing polymerization and removal of a substance having a lower boiling point; thermal coloring occurs; and the like. When the average temperature raising speed is 0.5xc2x0 C./min. or more, a resin is sintered and grinding into a granule may become difficult, and even if sintering does not occur, problems on physical properties may occur.
The raising end temperature (Axc2x0 C.) is preferably (FT0+100)xc2x0 C. or less, and further preferably (FT0+80)xc2x0 C. or less, for uniform polymerization of a granule or pellet of a resin.
In the step (1), a resin is so heated that the flow beginning temperature (FT) of a thermotropic liquid crystalline resin at each resin temperature (t) is (txe2x88x9210)xc2x0 C. or more and (t+40)xc2x0 C. or less. Even if the average temperature raising speed is in the above-mentioned range, when FT is over (t+40)xc2x0 C., polymerization and removal of a substance having a lower boiling point may become insufficient. When FT is lower than (txe2x88x9210)xc2x0 C., a resin is sintered and grinding into a granule may become difficult, and even if sintering does not occur, problems on physical properties may occur.
For example, a method which satisfies conditions such as the above-mentioned resin temperature and flow beginning temperature includes a method in which a resin having flow beginning temperature of 260xc2x0 C. in which (I): (II): (III): (IV)=500:250:237:13 heated up to 230xc2x0 C. over 70 minutes, subsequently heated up to 330xc2x0 C. over 300 minutes.
Further, it is preferable that the process of the present invention further comprises a step (2) in which the resin temperature is lower to 200xc2x0 C. or less after the resin temperature reaches the raising end temperature (Axc2x0 C.). The average temperature lowering speed is not particularly restricted, and preferably 0.5xc2x0 C./min. or more when the temperature is 200xc2x0 C. or less.
Further, it is preferable that the process of the present invention further comprises a step (3) in which thermal treatment is conducted for 1 hour or more at a resin temperature within Axc2x0 C.xc2x110xc2x0 C. and a variation of a resin temperature within xc2x10.1xc2x0 C./min. after the resin temperature reaches the raising end temperature (Axc2x0 C.).
By adding the step (3), the molecular weight distribution becomes narrower and polymerization and removal of a substance having a lower boiling point can be attained sufficiently, by uniform polymerization of a granule or pellet of a resin.
Furthermore, it is preferable that the process of the present invention further comprises a step (4) in which the resin temperature is raised from any temperature of not more than 200xc2x0 C. and less than (FT0xe2x88x9240)xc2x0 C. to any temperature of (FT0xe2x88x9240)xc2x0 C. or more and (FT0+20)xc2x0 C. or less at an average temperature raising speed of 0.5xc2x0 C./min. or more, before the step (1). By adding the step (4), the treating time can be shortened. Particularly, when raising of the resin temperature is initiated from normal temperature (around 20xc2x0 C.), and the like, it is more preferable to conduct temperature raising at a rate in the range from 3xc2x0 C./min. to 10xc2x0 C./min. for the purpose of shortening of the treating time, and the like.
When raising temperature at an average temperature raising speed of 0.5xc2x0 C./min. or more up to temperature over (FT0+20)xc2x0 C., a resin is sintered and grinding into a granule may become difficult. When temperature is lower than (FT0xe2x88x9240)xc2x0 C., the heat treatment time may become longer. In the step (4), it is more preferable that temperature raising is effected at substantially constant speed.
As a method of introducing a resin into the step (4), the following methods are listed.
(a) A method in which a resin leveled on a tray is introduced into a compartment type oven, then, heated at a temperature raising speed of 0.5xc2x0 C./min. or more up to a temperature of not more than (FT0+20)xc2x0 C.
(b) A method in which a resin is introduced into a rotary kiln pre-heated to a temperature of not more than the flow beginning temperature (FT0+20)xc2x0 C. of the resin.
(c) A method in which a resin is continuously introduced into a fluidized bed type drier having a resin introduction port controlled at a temperature of not more than the flow beginning temperature (FT0+20)xc2x0 C. of the resin.
(d) A method in which a resin is introduced into a tunnel type conveyor furnace having temperature distribution, having a resin introduction port controlled at a temperature of not more than the flow beginning temperature (FT0+20)xc2x0 C. of the resin.
In the present invention, a metal oxide, organic metal salt, organic base compound and the like may be used as a polymerization catalyst. Examples thereof include, but are not limited to, oxides, acetates, oxalates and the like of germanium, tin, titanium, antimony, cobalt, manganese and the like.
In the present invention, an antioxidant, thermal decomposition-preventing agent, hydrolysis-preventing agent, ultraviolet absorber, flame retardant and the like can be added to a pre-polymer in an amount which does not deteriorate the object of the present invention and which does not exert a reverse influence on physical properties.
The thermotropic liquid crystalline resin composition of the present invention is obtained by compounding 10 to 100 parts by weight of an inorganic substance per 100 parts by weight of a thermotropic liquid crystalline resin according to the present invention.
As the inorganic substance to be compounded according to the object, general inorganic fibers such as glass fiber, carbon fiber, metal fiber, alumina fiber, boron fiber, titanic acid fiber, asbestos and the like; powder substances such as calcium carbonate, alumina, aluminum hydroxide, kaolin, talc, clay, mica, glass flake, glass bead, quartz sand, silica sand, wollastonite, dolomite, various metal powders, carbon black, graphite, barium sulfate, potassium titanate, calcined gypsum and the like; granules or plate inorganic compound such as silicon carbide, alumina, boronite light, silicon nitride and the like; whisker and the like are listed. Among them, glass fiber and carbon fiber are preferably used from the standpoints of strength, rigidity and heat resistance of a molded article obtained by molding the composition. A thermotropic liquid crystalline resin into which the above-mentioned inorganic substance is not compounded may not be used for obtaining a molded article having stable form due to excess anisotropy.
In this composition, an antioxidant, thermal decomposition-preventing agent, hydrolysis-preventing agent, ultraviolet absorber, antistatic agent, coloring agent (pigment, dye), surface treating agent, conductor, flame retarder, lubricant, releasing agent, plasticizer, adhesion aid, sticking agent and the like can be added in an amount which does not deteriorate the object of the present invention and which does not exert a reverse influence on physical properties.
Further, a small amount of thermoplastic resin, for example, polyamide, polyester, polyphenylene sulfide, polyether ketone, polycarbonate, polyphenylene ether and modified resins thereof, polysulfone, polyether sulfone, polyether imide and the like, and a small amount of thermosetting resin, for example, a phenol resin, epoxy resin, polyimide resin and the like can also be added alone or in combination thereof.
When the thermotropic liquid crystalline resin composition of the present invention is processed into moldings, the deflection temperature under load of this moldings is preferably 300xc2x0 C. or more.
In the case of use in a coil bobbin which is soldered by direct immersion into a melted solder, supporting members for electric heat bodies and light and heat instruments of high temperature, and the like, the deflection temperature under load is preferably 330xc2x0 C. or more, and more preferably 350xc2x0 C. or more.